Problem: In 42 years, Jessica will be 3 times as old as she is right now. How old is she right now?
Answer: We can use the given information to write down an equation about Jessica's age. Let Jessica's age be $j$ In 42 years, she will be $j + 42$ years old. At that time, she will also be $3 j$ years old. Writing this information as an equation, we get: $j + 42 = 3 j$ Solving for $j$ , we get: $2 j = 42$ $j = 21$.